Signaling-circuit.



G. A. CAMPBELL. SIGNALNG clncul.

APPLICATION FILED MAYI8. {9i-TF 1,254,476. Patented Jan. 22,1918.

2 'SHEETS-SHEET n.

TTORN EY vention; while ,an arrangement the over-all efficiency is a maximum when the resistance of the receiver is equal to that of the transmitter. When this condition is satisfied, obviously fty per cent. of the energy delivered by theline to the substation is wasted in the transmitter' and fifty per cent. of the energy delivered by the transmitter is wasted in the receiver. Further, such an arrangement labors under the disadv Lntage offull side tone. In the substation of 'my invention fifty per cent. of the energy delivered by the line to the substation is wasted in the transmitter but none in the auxiliary resistance if said auXiliary'reSstance and said` line are conjugate; hence ,the efficiency of receiving is as great as that of the simple series substation. When transmitting no energy is wasted in the receiver but fifty per cent. of the energy delivered by the transmitter is wasted in the auxiliary resistance. The transmitting eiiiciency is therefore also a theoretical maximum and' neither transmit' ting nor receiving eiiiciency is reduced by the additiony of the auxiliary resistance which is necessary to secure freedom from Vside tone. The foregoing consideration will serve to explain the desirability of having the line and auxiliary resistance conjugate as well as the transmitter and receiver.

In my presentinvention I provide a substation `comprising transmitter, receiver.,

auxiliary resistance and transformer, and sof proportion said, component elements and so 'relate them to a telephone line and to each other that, in combination with said telephone line,.said substation satisfies all of the foregoing requirements.

I have discovered that the above-mentioned requirements may be satisiied by a large number of arrangements employing the minimum number of elements and all equally efficient and Without side tone. While theoretically all these arrangements are equally good, practical considerations make certain arrangements preferable'.I

My invention is best understood by reference to the accompanying drawing in which Figure l is a diagram illustrating one formi.

of my invention; Fig. 2 is a diagam illus-l trating the operation of the substation of Fig. lduring transmission; Fig. 3 is a similar diagram illustrating the operation dur# ing the reception of signals; Fig. 4 is a diagram illustratin a modification of my inlgigs.- 5 and 6 are diagrams illustrating thepoperation of the substation of Fig. 4 during transmission and =reception respectively..

Referring lto Fig. 1, 'a telephone-line L terminates in a` substation comprising a transmitter T, areceiver R, an auxiliary resistance X, preferably,.non-inductive, and a transformer having windings A, B and C.

Said transformer is preferably of very high impedance and very closely coupled conditions, 'it is Well known, which may be very approximately satisfied in telephone transformers. sistance of said windingsl be negligibly small. l/Vhen direct current is supplied to transmitter T frein line L, a condenser 5 may be inserted in series with Winding B in order to confine the direct. current to the transmitter. Said condenser 'may be, so large as to offer very small reactance to currents of telephonie frequency, or its capacity reactance may be substantially neutralized by the inductive reactance of the winding B. In either case the capacity effect may be rendered negligible as regards telephonie currents. As shown in the drawing, line L, winding Cf, auxiliary resistanceX, receiver lt and transmitter T, are serially connected. Winding B is bridged across the junction points of the line L and the transmitter '.l" on the one hand, and the receiver R- and the auxiliary resistance X on the other hand, at terminals 8 'and 6 respectively. The winding A is similarly bridged across the junction points of thetransmitter T and the receiver R, and of the line L and winding C at terminals 7 and 9 respectively.

Referring now toF ig. 2 the arrows indicate the direction of current flow during transmissionand the dotted lines indicate elements through which no current Hows.

In said` diagram, as well as in the dia- 1 grams of Figs. 3, 5 and 6 and in the equations and formulae hereinafter given, the subscripts 1, 2, 3 and 4 refer to transmitter,

receiver, auxiliary resistance and line, re-Y spectively; thus Il, I2, I, and I, denote the currents flowing inI the transmitter, receiver, auxiliary resistance and line, respectively. In interpreting said diagnams it shouldI be understood that the direct battery supply current which is preferably supplied over the line from a central source of energy is not indicated since said current merely serves 4to energize the transmitter.

Further itwillbe understood that the flow of telehonic current as indicatedby the arrows s conditioned by the proper proportioning of the component elements of the substation in accordance with the design formulae herein after derived and set forth.

Theoperation during transmission isin dicated in Fig. 2 and is as follows: The

lao

actuation of the transmitter T sets up varia-.

tions in the resistance thereof which are equivalent in their action to an alternating electromotive force in said transmitter. An alternating current of telephonie frequency is therefore superimposed o n the Ndirect current (not indicated), the path and relative direction of vsaid alternating current being indicatedby the arrows. Slnce the substation 1s without side tone no current flows through the receiver; but the total alternatingcurrent in the transmitter, denotedby I1, 'flowsfjfrom terminal 7 'through .winding A to terminal 9.y Here the current divides, a portionl flowing out over line L and back to termina 48 of the transmitter; while n.

portion I, flows through Winding C, cuxillary resistance X and winding to terminal 8*-Wh'cre it joins the returning line current Il.' ItjWill bef clear that the transmitter.

current I, is equal to the eUni'uf the line 'current' L and the current I, which [lows through the auxiliary resistence X. Said current I', is wast'ediin the resistance X, but.,

es herein shown, such waste is unavoidable proportioning of the relative impeflsinces of line and auxiliary resistance with reference to the vrelative number of turns on windings of the transformer. The windings, when properly proportioned., interact in such munnervthat potentials are induced in the windings B and C in a direction tending to increase the potential of `terminal C to n value-equal to that of terminal 7.

Referring to Fi 3, which is n. diagram villustrating the re stive directions ci vflou-f of telephonie current during the opcrctimil of receiving, e potentiel npijiictito the line causes a current L to flow over the .line L This current then Hows through the Winding A. to terminati 7,

thereby inducing n. current l, in Winding B Whihfio'we in the opposite diizeci'zion, ,scid current. flowing from termine-Il. E through Winding B andj receiver It to terminal 'T Where it unitee with. current LL so that a current 1,. eqncl `to the combined current-s` I2 and I4 flows through the transmitter 'l to terminal 8. At this point the current divides,A the portion L, flowing bach over thelinc while the portion l flows through the Winding B,f s'el1cady described. No current flows' through the auxiliary resiet` 'ence X when. the elements of the substation are properly proportioned .ce the potentials induced-in windings B und C urein such direction and ovsuch values es to raise-the .pctcntiei of terminati 6 to a value .equal to tilct of terminal l0.

Before proceeding to the Adescription cfa genero-l' the .modification shown in Fig. 4, 'theoretical discussion vwill* now liegiven which upplles .to'all substatons satis ving the requirements Aheretofore'j.stated in this j sj'iecilicutioni--' l v- .v This discussion, Which'illnstrates the scope 'station have4 maximum of my invention mil elncidetes1 the rinciples upon which allspecific .embodiments rest, will be followed sideration of the manner in 'which the urrangement of Fi 1' is pro ortioned, together with u derlvation of t e design for mulee applicable to said( erre' gement. In this discussion and the"eqflulationsand formulae'included in this specification, the'I subscripts 1, 2, 3 vund 4wiil, ashereinbefore stated, refer to transmitter, receiver, `auxiliary. resistance und line'prespectively.l Thus' I1, I2, I8, I, will denote the currents flowf ing in transmitter, receiver, auxiliary resist ance and line respectively, While R1 will denote the resistance ofthe transmitter, R2 the resistance of the receiver, etc.

lonsidci n substation consisting of trans mittel', receiver, auxiliary resistance und nppropriutc trunsffgnfmcr windings', connected to u line of givin impedance. In practice the lino connects two similar und equal sub? stations 'between which communication is established. It is u Well known principle that if n terminal impede-nce is connected to u source of eli-.ctrox'notive force through u line' of impedance 'r'zltrl-eRi, Where R4 is the resistance und. it', the renctance com@ ponent of the impedance, the terminal im` pcflnncc must. be lip-RQ for maximum uhsorption. of energy. In particular if the line impedance has no -recctunce component, the impedance ofthe terminal arrangement as seen 'from' the lino should be equaljfto the resistance component ofthe impedence of the line. The condition, that the -snbstation sho-ll have maximum energy absorption from the line is that ite impedance, es Seen 4tronc the lino. shall lie equal to the line impedance. The significance of the foregoing statement muy be explained by reference to Fig. 1 .us follows: Let the sub station be disconnected from the line :1nd

" let,the impedance of the suhstatonbemeas nred lacross terminals 8 and 9.- Then the impedance so zineesuredshell. be 'equal to the impedance ofthe liney AV-Vith the line ter mina-ted et each 'end by e substation satis fying this condition, the linel .may locreplaced, as regards substation., hy animpedence element ofv retransmission from either L by theoretical conlill) sistance equal to the impedance of the line.

Any reactonoe effect, which is in practice smell, mayfbe eliminated by neutralizing reuctance and, therefore, need not be con- Sidered; The condition,then, that the subenerg absorption from the -line is that its i-rnpe/ence es 'seen from the line bene pure reslstancc 'of value equul. .to the impedance ofthe line. This v.condition is'evidently equivalent to the fol@A -lowln l requirement; 4Loten. electromotive force e impressed -onthe'snbstaton termifnclr tlrr'outgh-V c resistance Ee nel .to the iur pedance o the line; their t e energycorhA Cir sinned in the eubstation shall be equal to tbe energy consumed in Suid resistance.

l `urtl1er, line and auxiliary resistance are conjllgute by requirement "es+'l1iereinbe-A teutiul with Jee'peet toen eleotroulotiveforce station whose 'trnnelni'tter and receiver ire# slet-nume"- nnd receiver be I L-,jll and I2 respectively; then the inlpledu'ncfeaeross tle substation terminals nul-5t be R4 es eeen from the line'end tlie `total resistunee in series with E4 is 2RM' und eine@ ille euri-ent in the line is I4, it follows that l E .eM-4 =L R4 Sumpf/ion in tle resistentie R4' yis equal to that in the substation, and that the Substa-y tion is eqnivnlentygrs seen' from tl'ie line, to u resistance ot" velue R4. 'Y A Silnileily it transmitter" and receiver are conjuga-te, thefonditionthztt the transmitter slmll-lmveite maximum output to 'line and auxiliary resistance may be formulated as follows: en eleetroniotive; force ,EL in the transmitter produce' eurrents Il, 14 und la in transmitter, lineend auXili-(try resist? ence. Then, for maximum output, it fol- Equation A(2) I istbe analogue @of-equation# (l )5 end/nitty i be interpreted ae follows? by t'ore stuted or in other wordethfe auxiliaryi resistance is eonueetedtopointent-.lequel po-ll'- Ar v. M 7l, ,i 4. ,l i let the' resultanteurrents:1nl1ne, transmitter feneewlientransmitting. vllet-TVVL, be the total This equationStetestliet the energy een* referenoeMto Fig.. l.' Letftlie'Y foonduotor which connecte transmitter .'I toterr ninel '7 y i' be opened je-nfl letth'e impedance be,,xfree8-A t'reneinitter itself. In other Words the impedanee ofA the combination, es seen from the traneinitterz is equal to that of the transl.' ire' .L; $1.31 gir-55 1' Asheiieinzftershown for'tlie lpertinlr* 70 embodiments ofmy invention,'equetidff)lav I follows es a consequentie of the eonditidivilff double oonjugeey eind 'equation (1)5 "Mlril'ieeL ore the foregoing-'four requirementlsi'ipe" butv three" restrictions onthe subetaltiol .s To'oom'plete'tlie generel disloussion'iit'rmains to "e'onside'r tlie'ene'rg'y dii/ieonjbertween recentery 1nd vtrenfsniitter when' 'receivng Pz'tndbetwee'n line fend' S uxiliairy' re'sistv i amount oftolephonieenergy 'levelfjedby' the transmitter ut tbe 'transmitting:siibs'tul tion; `tlien by equ'a'tim '(2),'l/27V5 visy the amount of energy delivered jto/line and .aux-

iliary resistance. Let the finibutof energy taken by the auxiliary resistencia be times that taken by the line, tlien` tbe amount of energy taken by the line is'A j '5 5 so that the transmitting' eticienoy is measured by 1 'Q Y 95 I (i (U) y y the tota-l energy -deliver'edto the receiving substation, let the'trensinitter absorbg/ ltimes that absorbed by' receiver; then 100 tbe reeeiving efficiency/is measured by oierfell elieieney would be e maximum for nfzyztl For all substetions embodying the lll) principles of my invention it may be reclil'y shown, however, that :v and y are eonnectenilfql by the. relatlonyrl. Eliminating m from tbe above .formulaJ byfmeens of this' relation,

,.lheexpreesionfor the over-ell efficiency bewerbefrei Y.; t i.

wie@ fr Multiplying equation (1 tion (2') by R, and subtracting,

Langue branches 3 and 4:, it follows that sier-suza Also by equation (1) 'l v 1- 1 (844)2134 (SizyRx 'l'SnlzRi um (1,)

4Rt and by equation (2) i (Suv-R1 :"(SilayRa 'l- (S14)2R4=m1 (2 lt is a 'lundziincntal principle which is deducible from elementary algebra, that S411: Th1-it is, the current sel: up in branch l by n uiii' electroinoiive Torce in branch i4: is equal to the current set up in branch L1 by a unit electr-emotive force -in branch l.

) hy 'R4 and equait follows that: v i

4(S42) zRzRi: (Sir: 01)

. New in accordance with the notation adopted in this specification, the energy consumed in branch 3 is a: times that consumed in branch 4 when an elcctromotiveforce acts in branch 1 g' therefore (aoiRFuScrRi e).

Also, the energy consumed in branchl .is i/ times that consumed in branch QWhen an elcctroirrotive force acts in branch 4 ;.l whence (S14) zRilzl/(Sze) 2R@ (0) Muiublying (b) and (ff) Fremde) and.(a) it follows at once that wgfzl,`

Obviously I'the expression lgiven by for- A mula '(5) is a maximum when z/zl. This energy in the receiver is the prime desider-A atum of telephony, it would appear that the substation 4should be designedto make y=1.

Another consideration, however, modifies tlfj s conclusion. somewhat, namely, theelfect :1A line noise, Since the line noise origin es 4will equal zero.

in the .line the amount delivered to the, receiver is proportional to (seeielquation et) While `the amount of energy delivered from the" transmitter of the communicating station isproportional to (1 HD (see equation 5). The ratio of the latter to the former is and .this -increases as y increases beyond unity. It will be clear, then, that if y is made greater than unity the substationl discrimination against line noise as compared with the signals it is desiredto receive. The amount of discrimination desired depends of course on the amount of line noise present. For conditions occurring in practice I have found by experiment that a desirable value for y is 1.4. With this value of y; the over all efiiciency is reduced 2,8% below the maximum for yzl, while the receiving efliciency alone is reduced 16.6%. tain conditions it may be desirable to sub stantially increase the valueA of y beyond unity. It will be therefore understood that, when the value of y is referred to as approxi mately unity, its actual value may considerably exceed the theoretical optimum.

The above consideration as to over-all ezt- Iiciency and discrimination against line noise may be formulated as for; an electromotive 'force inserted in the with respect to transmitter T is satised if 'Ano current flows in said receiver m' consequence of an electromotive force# `f telephonic frequency inserted in series wiith the transmitter between terminals 7 and' 8. If receiver R is to be conjugate to said transmitter then points 6 and 7 must beat the same potential as regardsthe effect bf said electromotiveorce. Further if the windings of the transformer have ve impedances, the algebraic sum o the ucts of the currents flowing in said Win ings, by the number-of turns of said windings,

Bearing these considerations in mind, the condition fof conjugacy' of 'transmitter and receiver is derivable' as fol.

Assume an electromotive [force -in the However under certransmitter branch of Fig. 2, and let I, I27 I), and I4 denote the currents flowing in transmitter, receiver, auxiliary resistance and line respectively. Then silice no current flows through the recieivei` I Also if the self'impedauce of the transformer is very higlnreprescnting the ninnlier ot turns of windings, A, B and C as a, I), and c respectively lfb-olf Since IZrIl-Il this equation heroines Wh ence Ii .l denotes the voltage drop per tuin in the transformer windings. Y the potential.

difference across the terminals of the transinitter, and R1, R2, It., and R4 the resistances ot transmitter, receiver. auxiliary resistance and liiieirespectvely, it follows thatfsiiice points and 7 are at. the saine potential;

Also, since the impressed potential is equal to the algebraic suni of the I R drop through the line and the drop through windingI A.

vz-KHLR) (io) 'lhe negative sign indicates that the induced drop through winding A is iii the opposite direction to the current tlow therethrough.

Furthermore since points (i and 7 are. at the same poteiitialrthe drop between each ot Said points and point 9 must lie equal so that IBRBiKCzKa 'llio several equatii'ins just derived troni i Fig. reduce to the following relation which must. be. satisfied for conjugarvof transmitler and receiver;

where R., and'l4 are the resistance of auxi|i:ir \T resistance and telephone 'lino respectively.

Similarly, referring to Fig. 3, theI condi-V tion of conjiigacy -of line `and auxiliary resistance may be derived as follows: `'Assiimiiig an electromotive torce V applied across the terminals 0f the line, since no current flows through the auxiliary resistance Iz() and IlzIZ-t-L (13) Since the algebraic sum of the products of the currents flowing through the 'transformer windings by their number oi ,turns is zero zI4JJI2=O Combining this equation vwith the preceding We get 'a b 11:( "5)14 (145) Further, since the applied voltage equals the algebraic sum of the induced drop through the winding A and the I R drop through the transmitter,

The several expressions derived from Fig. 3 niav be reduced to the following expression X n satisfying the requirement of conJugacy of the. auxiliaix7 resistance with respect to the line;

= R1@ (is a) (19) where R2 and R, are the resistance of 1'@- ceii'er and transmitter respectively.

From equation (8) it is apparent that during transmission I4 and I1 are. proportional to it-o o and i-l-o respectively` and since from equation (7) above I .izIl-Iq, it is evident that I g is proportional to a. Substituting these values in equation (2) the condition oi niaxinium output oic the transmitter is satised by the following expression vRi z`i'Ri(b"i- 'a)2v which reduces to lSimilarly., during reception it,l is apparent from equation (14) that Il and I4 are proportional to niet?) and L and since from equation (lit-l) I. ,::I1--Ii it follows` that I2 is `proportional to a. Substituting these valiies mamas in equation (1) the lcondition that the receiver shall have maximum energy absorp tion from the line may be expressed: RI a* R101): Rita' b)z Rdmmutlcfg (2.1:) So also by substituting these values in equation (6) we have as the expression for' maximum over-all efficiency Denoting land by 1' und r respectively equations (19) and (22) give effen efe) @merry- 1) Equation v(23) by simple-:rlgebraie transformation beeomes Ltr: '"(Ltr) `Dividing equation (25) by @quante (24j)Y we have (r-{Tl Multiply-ing equzition (24') uml equation i (25)- We have -Rm (1) 2" ly SubstitutingL?n and 'ff' in equation (12) said-'equation m'ny be rewritten Fig. 1. -above deslgn formulae the wmdmgratlos r replaesthej auxiliary resistance of Fi`g v l.

' ultplying equatins (23) and (28) we have By substituting r and r for endg in equations (21) und (22), undelimineting'R1 from said eiiimlienewe have T2 Rzm'l'-R (30) If now in equations 26, 27, 29 and 3A()V *I i@ be written as F and be written as It, then said equations may be written as follows:

fit1

Ri 'Ra/1min .RFM- i 1+y) l) The above group of formulae are the fermuhe appropriate to the substation of It will be observed that, in the will be seen that-they are identieztldexeept1. for the interehnnge of certain component elements. Thus in Fig. 4 the transmitter T.;

replaces theline of Fig. 1, the receiver of Fig. 4 replaces the transmitter f Fi 1,

the nuxilinr'y resistance X-of Fig.=4 're aces,

the receiver of Fig. 1 und the linefof dg.' 4

transmitter .T 'Set up veretiiisinfthefresietf -nnce thereof whh are equiyalentiin Itheir 'with Fig. l;

action to an alternating electroinotive force rent I] therefore flows from' terminal fi through winding B and through transmitter" T to terminal 9. A potential is'thereby induccd in winding A so that a current I, flows from, terminal 6 through resistance X and winding A to terminal 9. At said terminal the'eu'rrentsl'1 and L join'so that :i current I4 flows lfrom terminal 9, through Winding C and over line L to terminal 6, at

Which point it divides so that currentsl1 and I3 flow throughthe transmitter' and auxiliary resistance X as already stated. ,No current flows through the receiver R, this result being effected by the interaction ott the transformer windings, potential oli such value and directionbeing induced in windings A and B as ,to bring points 7 and 8 to the same potential.

The action during reception is; indicated in Fig. G. Assuming a source of current vaA riation applied to the line terminals, at a given instant a current L flows .from terminal l0 through winding G to terminal 9 where vit divides, a current I, llowing through'transmitter T to icrminal, und a current l2 .flowing through winding A and receiver l to terminal 8. At this point the. euri-ents l, and lzfinerge, 'and a current I, Hows from the terminal 8 through the windingll back to the line. No current Hows `thro-ugh the`auxiliary resistance X as the windings of the induction coil are so propern tioned with'respect to the resistances of thc line, transmitter and receiver, that poten tals will be induccdy in windings A and B of such value and direction to bring points 6 and `7 to' the same potential.`

' 'The design formulae in accordance with which theeleincnts offthe substation of Fig4 4c may be proportioned to secure the results herein set-forth maybe derived in a manner analogous to that described iii-connection Saidl design formulae' are as e subs-tations ldrstclo. above'fand ill us;

trated in Vthe accompanying -drawingarc' but two of a large number employing only one transformer and oneiauxiliary resistance and all oi' .these are ideal' in the sense that they satisfy the fundamental requirements for an ideal substation, as stated heretofore in this specification. It will be understood therefore, that my invention is not limited =to the specific embodiments herein illustrated7 but is broadly directed to providing a substation comprising a single transformer and only one auxiliary element, which is so proportioned with reference to the line with which it is to be .cooperatively combined, that it is ideally eflicient and substantially without side tone. Furthermore, l do not desire 'to limit the design of the substations herein disclosed and illustrated to the accompanying design formulan. These formulzc are derived ou the assumption that idealtransfoirrurrs are employed and that the component elements have no rcactance, assumptions which are only approxiinately justified in practice. Whe-u particularly high precision is desired, l may, therefore, proportion. the substation more precisely by taking into account the fact that the transformer impcdances are J(inite, and that the liuc and tho various substation elements may have in general some reactance. 'lhe accom partyingfforinulzc, however, give quite Satisfactory results, and the methods they are derived will enable one skilled in the art, to compute. inore precisely the substation. constants when desired.

lt will be understood thatin the appended claims, where certain elements are said to be conjugate, or certain impedance relations are 4said to exist, since in practice these conditions can, in general, only be approximated, these expressions will' be satisfied by strictures substantially conforming thereto, especially where some compromise with regard to 'the rigid requirements is necessary in order to discriminate against line noise.

lt will bc l'urthcr understood that While I have specifically illustrated and described my invention as embodied in a telephone. substation, itis capable of man-y and vaiicd Vembodiments which render it applicable in other kinds oi signaling systems and conscquciitlyiny invention is not to be Vlimited to tance .ati'clsonp windingoif the. transformer" by which i being connected in a series circuit, andf'the other'two windings bf said transformer belng bridged across said series circuit.

2. In a tWo way signaling system, a cir- -.c|iito,i j t he transiriission and reception of "signals, a traiismitt-mgcircuit proper,v a receiving circuit proper, a balancing circuit,

j Sistanoe anni minis trimsornier'linving three winin all of ssiglwoimuits end one of-,sscL'windin b 'ein sergiil'ly"relateel,-encl tlieother wni ping m bridge relation with respect to said'crrcllits, j

8. `In,:ombinr.tion with a.' telephone line, n substgition, said substation comprising o. transmitter, receiver, auxiliary resistance anda transito-"ner having three windings, saliti line', iitter.; receiver, auxiliary reono win .ng'o the transformen being connected in n. serios circuit, another f fof Said winding? being in slnnit of said line V and a transformer being:4 connoot .0

and transmitter, smith@ third Winding being in shunt of suf-.ifi fenetre-r e118, transmitter.

et. in comi.' s telephone line, n. substation, s substation comprising a1 transmitter, Irceoeircn, auxiliary resistance having three windings,

iter', auxiliary re'- o" the transformer circuit, another ged across- 'aid 'i vor and transsaid line, trs-ne sistanoe and on said wint-lio circuit in si: ont of? 1 l mltter anzi the mim .win-,img belngj'also bridged aorossssicl circuit. l i n sfftsm comprisulg. o tijsns'- 5. A signaling n former and 'four f nentsl elements foonsisting ofa path for is transmission and recaption of signals, s trsnsxnittingelement, a

receiving element, and a-belanoing element,

vseid fundamenta-l elements engi one winding of said transformer being in e.' series circuit.

.aty

6. A'signnling system ooniprising a. trans- :formr and four fundamenta elements oonssting of e path for the transmission and reception of signsis,s tronsinitting element, a, 'receiving ele1x1en.t,.a.nd e' balancing element, said'fundomental elements and one winding fofsnd transformer being in a` series ciroit,

said transformer 4and said' .fundamental ele -ments'being so'proportionerl and related that seid transmitting element and s'ztid receiving element are eonjngat A signaling system comprising av trnsformer and four fundamental elements conaisting of a path for the transmission and' reception of signals, a transmitting element,

' ment, ssi

element, and ai Balancing elefunda-mental .elements and one winding; of said transformer being inaf se rries oireuit, said transformer. and-said fundamental elements being-'so proportioned and .related that smid balancing element and said path ere'oonjugete.

8. A signaling' yawn-'comprising a transformer and four fundamenta sistlng of a. path for the transmisson'and reception of signals, a transmitting elelrn'ant,4

u; receiving element, und a balunoin element, said fundamental elements an one winding of said transformer being in a. series circuit, 'said transformer :1nd said fun damente] elements being so proportioned anni related' that theimpedanco of the combinetion comprising the' transmitting element, the receiving element, the balancing element, and the transformer, ns seen from said path, is equal to the'impeclnnoe of said path.

9, A signaling system comprising a. transformer and four frmduinental elements consrsting of apath for the-transmission and reoeption of signals, Vs transmitting element,-

zi receiving element, and a balancing element, sind fundamental elements o-f,'said transformer ibeing 1n a series cir Vcuitpfseid transformer and seid fundamentel"elements being'so proportioned :indre-l lateti that. thev impedance of the oonibinaion vj,'oonzqsiising 4said path, reeeiving element,

belanpmglelement and transformer, as seen Y fromthe trsnsmittng element, is equal 'to 'the inipeclance o f the transmitting element.'

10. A signaling system comprising a.

and one WindingV elements con? transformer snclfour jfunflumental elements consisting of :rpath forfthe transmission :rnd reception of s ment, n receiving, ement, and a balancing element, seid fundnmental'eleinents and one winding ofsaicl transformer being ina. series oirouit, ,said transformer and ssidxfnm damentnl elements being LAso proportions@ endI related that said transmitting sind receiving elements are conjugate; said path and stud' balancing 'element are conjugate; the impedance of the combination com risingsoicl4 inels, o. trnsmitting ele name to this Ispecification this-fourteenth lday of'Mey, 1917. I

GEORGE A. CAMPBELL. 

